Method and means for electro-optically photographing sound and sound track resulting therefrom



June 5, 1934. E HANSEN 1,961,610

METHOD AND MEANS FOR ELECTROOPTICALLY PHOTOGRAPHIN SOUND AND SOUND TRACK RESULTING THEREFROM Filed Aug. 12, 1932 INVEN TOR Patented June 5, 1934 UNITED STATES PATENT OFFICE Edmund H. Hansen, Los Angeles, Calif.

Application August 12, 1932, Serial No. 628,538

Claims.

The hereinafter described invention relates to the art of electro-optically photographing sound and deals with a method and a means particularly adapted for use in the variable density method.

5- It is the primary object of this invention to provide a method and an apparatus for producing sound tracks of the variable density order wherein there is no light value present during silent intervals, the consequence of which is to materially reduce ground noise.

In the conventional type recorder wherein noise reduction is accomplished by means of biasing similar to that shown in applicants copending application Serial Number 535,054, filed May 4, 1931, there are many disadvantages. 'These have been eliminated for recording in the variable area method as shown in another of applicants copending application Serial Number 551,896; filed July 20, 1931. However, there are certain features of noise reduction that are also desirable in the variable density method. The method herein described is deemed a substantial contribution to the art through its ability to function without additional electrical circuits of the biasing type. Another feature of my invention is 'that my system does not follow the speech envelope, but functions automatically in response to the speech impulse itself. The simplicity of a mechanical adjustment over that of a complicated electrical net work will therefore, become apparent as the description proceeds.

As now practiced, the variable density method consists in light efiecting a traveling light sensitive base by a light source whose intrinsic light value is varied in accordance with the frequency and amplitude of an incoming electrical wave representing the sound to be recorded. It is usual to employ either a light valve, a mirror oscillograph, or a glow lamp in recording. In the case of the mirror oscillograph and the light valve, the normal unmodulated position of these devices is such that an unmodulated track value of fifty per cent of the total is produced. This introduces light values in the track during silent intervals and increases the ground noise. In the 'use of the glow lamp, a direct current is introduced, the value of which is half the full value for peak modulation. This direct current light effects the film in common with the signal and .50 forms the unmodulated portion of the track. In

all cases, the resulting track is a ladder like striatic structure of varying density.

I propose to provide a method and an apparatus which will produce a sound track substan- 5 tially identical in form with the foregoing described track, but one wherein there is no unmodulated light values present during intervals of no signal and one which may be used in standard equipment without any change in the equipment. In accordance with the preferred form of my invention, I use a single mirror oscillograph and control the swing of the oscillograph mirror by the incoming electrical wave which represents the sound to be recorded. A pair of vertical light beams are transmitted to the oscillograph mirror and are reflected therefrom onto a specially shaped mask in such a manner as to cause the beams falling upon the mask to have a vertical spaced relation. In practice, the beams should be thin vertical lines of light, substantially one milliinch in width, and may be produced from a single light source by means of prisms or reflectors suitably positioned, or they may be produced by two light sources angularly spaced. In conjunction with either arrangement, I employ the usual apertures and light condensing systems. It is to be understood that the beams of light should be of substantially the same intrinsic light value.

In the method as outlined in the foregoing paragraph, the two light beams are used to transmit light values to a light sensitive base in accordance with the frequency and amplitude of an incoming electrical wave representing the sound to be recorded. This is accomplished by the use of the mask in conjunction with the oscillograph. Briefly stated, the oscillograph operates to swing the two vertical beams in unison with their spaced relation, transversely with respect to the film travel. As the beams are swung across the mask, the mask serves to add positive and negative increments of light to the light transmitted to the film. In other words, as the oscillograph swings positive, positive increments of light are added to the light representing the negative portion of the wave and as the oscillo- 95 graph swings negative, negative light increments are added to the light representing the negative portion of the wave. The process may thus be said to be additive, wherein positive light values are added throughout both the positive and negative swing of the signal wave and the end of the maximum negative swing of the signal is the zero point of light value. During the time of no signal or when there is no oscillation of the oscillograph, the beams are arranged to come to rest behind masks that completely out off any light from reaching the film. This means that at the time of no signal, the track will be completely opaque in the positive print and no sound, such as ground noise will be possible during silent intervals. Also by eliminating the unmodulated portion of the track during the recording of sig nals, the introduction of ground noise is further reduced.

The specific apparatus employed in practicing my invention may take a variety of forms. For example, I may use one oscillograph with a single light source, or one oscillograph with a double light source, or two oscillographs with either a double or a single li ht source, the object being to produce two vertical light beams which swing in unison with a fixed spaced relation. With any of the above mentioned means for obtaining a pair of vertical spaced beams, substantially the same mask is used, the optical systems of course being varied to suit the arrangement used.

It accordingly becomes another object of this invention to provide a method for producing a sound track of the variable density order wherein two vertically spaced vertical light beams are utilized to add positive and negative increments of light to the light transmitted to a light sensitive base.

Another object is to provide means for practicing the invention.

Still another object is to produce a sound track of the variable density order wherein no unmodulated light values are present during silent intervals.

Other objects and advantages will become apparent as the description proceeds in conjunction with the drawing in which:

Figure 1 is a schematic view showing the preferred form of apparatus for practicing my in vention Figure 2 is a graphical representation of a sine Wave;

Figure 3 is an enlarged view of the mask used in my invention showing the position of rest of the two beams;

Figure 4 is the same showing the position of the beams at the end of the negative swing;

Figure 5 is the same as Figure 3 showing the position of the beams at the end of the positive swing;

Figure 6 shows another form which the apparatus for practicing my invention may take;

Figure '7 shows still another form of apparatus for practicing my invention; and

Figure 8 is a, fragmentary view of film carrying the sound track produced by my invention.

Referring to the drawing and particularly to Figure 1 wherein I have chosen to illustrate the preferred form of my invention, it will be observed that the apparatus consists of an oscillograph, generally designated A, a receiving and amplifying unit, generally designated 13, a light source and optical system for supplying light to the oscillograph, generally designated C, and a light condensing system, generally designated D, all of which will be more specifically described hereinafter.

As illustrated, the oscillograph A is equipped with an ordinary oscillating mirror 11 and the oscillograph is connected to one side of an output transformer 12 which in turn is connected to the receiving and amplifying unit B. The amplifying unit B may be connected by leads 13 and 14 to any electrical source representing the sound to be recorded. It is to be understood that the receiving and amplifying unit B may represent the regular equipment used in the electrical translation of sound.

The light source and optical system C may comprise as shown, a single source of light 15 supplied by a source of energy 16 and controlled by a variable resistor 17, together with two identical optical systems for splitting the light from the source 15 into two vertical beams 18 and 19. Since the optical systems are identical, a description of one will serve for both, the parts being designated by the same numerals throughout, but being primed in one system to differentiate from the other in the drawing. As shown, the optical system for producing the beam 18 comprises a prism 20 for intercepting and reflecting light from the light source 15, a vertical aperture 21 for confining the reflected light to a thin vertical beam and a convex lens 22 for condensing the beam before it is transmitted onto the mirror 11 of the oscillograph A. In actual practice, the prisms 20 and 20 are arranged to reflect beams from different fixed angles onto the mirror 11 so that the beams reflected from the mirror will have a predetermined spacing at a fixed distance from the mirror. As the beams are reflected from the mirror 11 they encounter a mask generally designated 23. As before stated, this mask is for the purpose of adding positive and negative increments of light to the light passing to the film in response to the positive and negative swing of the signal. Accordingly, the mask is formed with tapered apertures 24 and 25 and a rectangular aperture 26. For purposes of clarity and distinction, the aperture 24 will hereinafter be sometimes referred to as the divergent aperture and the aperture 25 will be termed the convergent aperture. Between the apertures 25 and 26 I provide a small vertical mask 27, the purpose of which will later be explained. Referring now to Figures 3, 4, and 5, the relation of the masks to the beams will be described. In Figure 3 I have shown the beams at the rest point or the point of no signal. Here it will be observed that the beam 18 is behind the small vertical mask 27 and that the beam 19 is behind that portion of the mask 23 which forms a mask between the apertures 24 and 26. Consequently no light can reach the film with the beams in this position. The positions of the beams at this point, I have designated 0 and O for the purpose of showing the relation of these positions with the phase of the incoming signal. In Figure 2 I have shown a typical sine wave and have designated the zero points of the wave 0. These points of the wave correspond to the positions 0 and O of the beams as shown in Figure 3. In Figure 4 I have shown the positions of the beams when the wave has reached the maximum positive point. These positions I have designated A and A to correspond to the points A of the wave, shown in Figure 2. will be noted that the full light value of both beams is allowed to pass through the mask. During the swing of the beams from the points 0 and O to the points A and A, it is apparent that the beam 18 passes through the rectangular aperture 26 and the full light value of this beam is allowed to pass to the film during this entire movement. However, as the beam 18 passes through the aperture 26, the beam 19 passes over the tapered aperture 24 and adds increasing increments of light to the beam 18. In this manner, the light passing to the film is built up to correspond to the full positive and negative value of the signal wave at any point. The tapered aperture 24 should be so arranged that at the end of the swing, or when the signal wave reaches the point A (Figure 2), which represents the maximum positive swing of the signal, the full light value of the beam 19 passes through the aperture 24. The

In this View, it

amount of taper given to the apertures 24 and 25 is immaterial in so far as the invention is concerned, and in practice will be controlled by the maximum positive and negative swing of the beams. The direction of taper for the aperture 24 should, however, be divergent with respect to the positive swing of the beams and the taper for the aperture 25 should be convergent with respect to the negative swing of the beams. After the signal wave passes the point A (Figure 2), the oscillograph starts swinging in a reverse direction and the beams 18 and 19 move back over the apertures 26 and 24 respectively. During this movement, the beam 19 subtracts increments of light from the full value of the light transmitted to the film, until the beam passes out of the aperture 24 and is out 01f by the mask between the aperture 25 and 26. At this point the beams are again in the positions 0 and 0' (Figure 3) and the signal wave has reached the half Wave position or the position 0 (Figure 2). It will be noted that the beam 18 at this point, transmits its full light value through the aperture 26. However, it is to be understood that the passing of the beam 19 behind the mask 23 and the passing of the beam 18 out of the aperture 26 are simultaneous. As the negative half of the signal wave continues to swing the oscillograph in the same direction, the beam 19 continues behind the mask 23 and the beam 18 enters the convergent aperture 25 and continues subtracting increments of light. It might be mentioned, that as the beam 18 passes over the small vertical mask 27 it is momentarily masked, but the time element and the width of the mask 2'? are so small as to be insignificant. The subtracting process is continued until the maximum negative swing of the signal wave is reached, which is indicated in Figure 2 by the letter B. The positions of the beams 18 and 19 for this phase of the wave are indicated by the letters B and B respectively, in Figure 5. This is the zero point of light value and also the point of maximum negative swing of the signal. In accordance with my method, only positive increments of light are added from this point upward, with the result that as the sine wave passes through the points 0, the light representing the half wave value of the signal has been realized and positive increments of light are added from this point up to the point A thus producing the full light value of the speech signal by adding positive increments of light throughout both the positive and negative swing of the signal.

After the light passes through the apertures in the mask 23, it strikes a convex lens 28 and from there is condensed onto a cylindrical lens 29 which converts the light into a horizontal beam and at the same time diffuses the light 15 over a horizontal slit 30. From the slit 30, the

light passes into a microscopic objective 31 where it is further condensed into the proper width and thickness and from the objective, the light passes onto a light sensitive film 32 where the light values are photographed to produce a sound track 33 of the nature shown in Figure 8.

In Figure 6 I have shown another form of apparatus for practicing my invention. In this form I use a single oscillograph A and the same light 5 condensing system D as previously described, but

in place of prisms for obtaining two beams, I employ two light sources 34 and 35 with the necessary apertures and lenses. The light sources should be angularly spaced in order to obtain a vertical spacing of the beams on the mask.

The form of my invention shown in Figure 7 are each provided with proper apertures and condensing lenses to produce a vertical beam from each source and the oscillographs are arranged to intercept the beams from the sources and refiect them into the condensing system D. With this arrangement I may use a single light source and arrange the oscillographs to intercept light from the same source at different angles and thus obtain the proper spacing of the beams.

The sound track produced by any one of the apparatus described will be of the conventional variable density type and may be used in conjunction with standard equipment without any changes made in the equipment. In addition, it is clear that the track will have no unmodulated light values present during silent intervals since all light to the film is out oil when the beams are at rest.

A method of the foregoing nature for producing variable density sound tracks is a departure from ordinary methods in that the sound track is produced by horizontally swinging a vertical beam and further that two beams are used to add positive and negative increments of light during the swinging of the beams.

Although I have shown and described a method and apparatus for producing variable density sound tracks of the novelty described, nevertheless I am aware that certain modifications and refinements could be made without departing from the inventive idea. I therefore reserve all rights to all such alterations in my method and all such substitutions of equivalent apparatus that come within the scope of the disclosure and the essence of the invention as expressed in the appended claims.

I claim:

1. For use in electro-optically photographing sound by transversely oscillating a pair of vertically spaced vertical light beams across a vertically moving light sensitive film in response to a signal: a mask having a rectangular aperture therein and two tapered apertures associated therewith in the manner described.

2. For use in electro-optically photographing sound by transversely oscillating a pair of vertically spaced vertical light beams across a vertically moving light sensitive film in response to a signal: a mask having a rectangular aperture and two tapered apertures therein, said tapered apertures being associated with said rectangular aperture on opposite sides thereof and having the taper thereof extending in the same direction.

3. For use in electro-optically photographing sound by transversely oscillating a pair of vertically spaced vertical light beams across a vertically moving light sensitive film in response to a signal: a mask having a rectangular aperture and two tapered apertures therein, said tapered apertures being associated with said rectangular aperture on opposite sides thereof and in a convergent and a divergent relation thereto respectively, and a small vertical mask between said convergent aperture and said rectangular aperture.

4. A structure as set forth in claim 3 and in addition thereto: a comparatively wide mask between said rectangular aperture and said divergent aperture.

5. An apparatus for producing sound tracks of the variable density order comprising: means for oscillating a pair of substantially parallel beams in spaced relation over a moving light sensitive base, and amask having apertures arranged to passlight from one. of said beams to produce the negative half of a speech signal and from both of; said beams to produce the positive half of said signal, said apertuiesbconsisting of a uniform aperture, a decreasing aperture and an increasing 

